The invention relates to an apparatus for forming a straight edge device when used with an elongate rigid member, such as a pipe, and a wire.
Straight edges are frequently used by millwrights, carpenters, bricklayers, fitters and pipefitters. The main use for a straight edge is alignment, such as the alignment of pulleys, and testing the flatness of surfaces. The most common type of straight edge comprises at least one edge of a flat bar of metal. If the bar of metal becomes bent or otherwise damaged, as may occur on a construction site, the straight edge is rendered useless. A worker commonly finds it necessary to have straight edges of different lengths for different jobs. Some tasks require a short straight edge in places where a longer one would not fit. The short straight edge would be useless where a long one is required. Accordingly, it would be desirable to provide a straight edge device adaptable to different lengths and which would not be subject to easy damage by accidents.
A telescopic chalk line in disclosed in U.S. Pat. No. 2,655,728 to Cook. In this device, the chalk line is stretched between a reel at one end of a tubular rod and arm at the opposite end of the rod. The line plays out over a small pulley. The device is not, however, capable of replacing a standard straight edge. The chalk line is not sufficiently rigid and would be too susceptible to sagging or deflection unless perhaps placed over considerable tension. However, the coil spring provided for tensioning the line would be insufficient for this purpose. Additionally, it should be noted, as seen in FIG. 2 of this patent, that the opposite wall terminus of the casing wall projects beyond the chalk line. Accordingly, it is not possible to have the chalk line lie flatly on a longer surface as may be required of a straight edge.
Similar devices are found in U.S. Pat. Nos. 4,202,108 to Adams; 2,788,584 to Adrien; 4,141,146 to Broom; 4,084,321 to Huston; 683,115 to Gilliom; 577,708 to Barrie and 4,228,588 to Horton. However, none of these devices provides a satisfactory solution to the problem of providing a straight edge device having a variable length for construction sites or the like, and which would not be susceptible to easy damage.